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Wednesday, May 18, 2016

Science has finally revealed what makes old books smell so good

I’m sure we have all wondered at some point in our lives – why the old books smell so good. And it is known that this characteristic smell comes as a result of a natural process of decay of things that make a book (paper, fibers, ink, glue, leather). The process that causes this decay is called oxidization, and depending on the level of moisture, heat or light – it can be sped up or slowed down.Namely, once the oxidization starts, materials that make a book release VOCs – volatile organic compounds, and these are actually that old books smell! These VOCs are as follows:

toluene and ethyl benzene, which give off sweet aromas

benzaldehyde and furfural, which smell like almonds

vanillin, which smells like — you guessed it! — vanilla

2-ethyl hexanol, which smells earthy and floral

Great, we now know what makes the old books smell so good; what’s the story about new books?

Well, it’s basically the same – the smell of new books comes from the materials the older books are made of, so paper and binding materials. But, unlike older books, compounds that make the smell of new books do not release these VOCs, and the reason for this lies in the fact that materials – paper, ink, glue, etc. – differ from one publisher to another (it can even differ from one title to another).

Compound Interest roughly explains the process of paper-making for new books:

The manufacture of paper requires the use of chemicals at several stages. Large amounts of paper are made from wood pulp (though it can also be made from cotton and textiles) — chemicals such as sodium hydroxide, often referred to in this context as ‘caustic soda’, can be added to increase pH and cause fibres in the pulp to swell. The fibres are then bleached with a number of other chemicals, including hydrogen peroxide; then, they are mixed with large amounts of water. This water will contain additives to modify the properties of the the paper — for example, AKD (alkyl ketene dimer) is commonly used as a ‘sizing agent’ to improve the water-resistance of the paper.

Now we know why the smell of new books differs and why it is difficult to distinguish what is what. It is all due to the chemicals that are used to prepare paper, ink, adhesives, etc.

As for the fans of old books smell – it may soon be a thing of the past, for today’s paper contains less lignin, which is a plant polymer responsible for that characteristic yellow shade of paper that comes with age.